I needed a real reason to stick to www not because it's shorter and it's easier to remember but I needed why would you pick www rather than non www.
Reason 1 : Check if google already indexed your pages
Check in google webmaster which website are most indexed already if 80% of the pages is indexed in that subdomain / naked domain then don't go further, that preferred domain is the winner.
Reason 2 : Cookies
It has something to do with cookies, even though i don't get it but it says... If you’ll ever need to go CDN or cookie-less for static resources, you can just use the workarounds. They aren’t any more complicated and also not a big expense.
if you’re planning on launching a very big website with potentially thousands of images and a lot of traffic, then it’s probably better to listen to your developers and go with the WWW version. It will make things a lot easier in the long run. (incognitiveseo)
Reason 3 : something to do with DNS
In order to not use www, you will have to run your own server farms and you will be unable to use such services to their fullest extent.
Redirection ensures that visitors who type in your URL reach you regardless of which form they use, and also ensures that search engines index your canonical URLs properly.
Now at least I have my reason to pick www subdomain, in seo perspective it is said that it's just the same but I want added value rather than same.